Dosimetry Phantom Research Articles

Modeling and dosimetric characterization of a 3D printed pregnant woman phantom for fetal dosimetry in radiotherapy

Modeling and dosimetric characterization of a 3D printed pregnant woman phantom for fetal dosimetry in radiotherapy

Monte Carlo modeling and simulation of a new 3D printed phantom for WBC calibration with ballistic gel as a tissue substitute

Whole-body counter (WBC) systems are used for in vivo monitoring in occupational internal dosimetry, typically calibrated using physical anthropomorphic phantoms. Our research group previously 3D-printed the Reference Female Phantom for Internal Dosimetry (RFPID) without internal organs specifically designed for WBC calibration. The RFPID and it is intended to fill it homogenously with ballistic gel, which is commonly used as a tissue equivalent in ballistic studies. However, comprehensive characterization of its physicochemical properties and radiological behavior as a tissue surrogate for dosimetry is limited. This study aims to evaluate the suitability of ballistic gel as a tissue substitute for physical phantoms in WBC system calibration and to analyze the RFPID as a model for WBC calibration. Ballistic gel tests determined its density and attenuation coefficients, comparing it to muscle, water, and PMMA. The RFPID was modeled and simulated using MCNP6.2 code and placed in an in vivo monitoring system using an 8”x4” NaI(Tl) scintillator detector previously validated. The simulations were repeated with the RCP_AF of ICRP-110. Results indicate that ballistic gel has a density approximately 6% different from muscle and shows similar linear attenuation coefficients to muscle at intermediate and high energy levels (186 to 2200 keV). Simulations revealed a disparity of less than 9% in counting efficiency between RFPID and RCP_AF for energies from 100 to 3000 keV, confirming the phantom's suitability for WBC calibration and ballistic gel's viability as a tissue surrogate in internal dosimetry.

3D printed heterogeneous paediatric head and adult thorax phantoms for linear accelerator radiotherapy quality assurance: from fabrication to treatment delivery.

This study aims to design and fabricate a 3D printed heterogeneous paediatric head phantom and to customize a thorax phantom for radiotherapy dosimetry. 
Approach: This study designed, fabricated, and tested 3D printed radiotherapy phantoms that can simulate soft tissue, lung, brain, and bone. Various polymers were considered in designing the phantoms. Polylactic acid+, nylon, and plaster were used in simulating different tissue equivalence. Dimensional accuracy, and CT number were investigated. The phantoms were subjected to a complete radiotherapy clinical workflow. Several treatment plans were delivered in both the head and the thorax phantom from a simple single 6 MV beam, parallel opposed beams, and five-field intensity modulated radiotherapy (IMRT) beams. Dose measurements using an ionization chamber and radiochromic films were compared with the calculated doses of the Varian Eclipse treatment planning system (TPS). 
Main results: The fabricated heterogeneous phantoms represent paediatric human head and adult thorax based on its radiation attenuation and anatomy. The measured CT number ranges are within -786.23 ± 10.55, 0.98 ± 3.86, 129.51 ± 12.83, and 651.14 ± 47.76 HU for lung, water/brain, soft tissue, and bone, respectively. It has a good radiological imaging visual similarity relative to a real human head and thorax depicting soft tissue, lung, bone, and brain. The accumulated dose readings for both conformal radiotherapy and IMRT match with the TPS calculated dose within ±2% and ±4% for head and thorax phantom, respectively. The mean pass rate for all the plans delivered are above 90% for gamma analysis criterion of 3% / 3 mm.
Significance and conclusion: The fabricated heterogeneous paediatric head and thorax phantoms are useful in Linac end-to-end radiotherapy quality assurance based on its CT image and measured radiation dose. The manufacturing and dosimetry workflow of this study can be utilized by other institutions for dosimetry and trainings. &#xD.

Development and first implementation of a novel multi-modality cardiac motion and dosimetry phantom for radiotherapy applications.

Cardiac applications in radiation therapy are rapidly expanding including magnetic resonance guided radiation therapy (MRgRT) for real-time gating for targeting and avoidance near the heart or treating ventricular tachycardia (VT). This work describes the development and implementation of a novel multi-modality and magnetic resonance (MR)-compatible cardiac phantom. The patient-informed 3D model was derived from manual contouring of a contrast-enhanced Coronary Computed Tomography Angiography scan, exported as a Stereolithography model, then post-processed to simulate female heart with an average volume. The model was 3D-printed using Elastic50A to provide MR contrast to water background. Two rigid acrylic modules containing cardiac structures were designed and assembled, retrofitting to an MR-safe programmable motor to supply cardiac and respiratory motion in superior-inferior directions. One module contained a cavity for an ion chamber (IC), and the other was equipped with multiple interchangeable cavities for plastic scintillation detectors (PSDs). Images were acquired on a 0.35 T MR-linac for validation of phantom geometry, motion, and simulated online treatment planning and delivery. Three motion profiles were prescribed: patient-derived cardiac (sine waveform, 4.3mm peak-to-peak, 60 beats/min), respiratory (cos4 waveform, 30mm peak-to-peak, 12 breaths/min), and a superposition of cardiac (sine waveform, 4mm peak-to-peak, 70 beats/min) and respiratory (cos4 waveform, 24mm peak-to-peak, 12 breaths/min). The amplitude of the motion profiles was evaluated from sagittal cine images at eight frames/s with a resolution of 2.4mm × 2.4mm. Gated dosimetry experiments were performed using the two module configurations for calculating dose relative to stationary. A CT-based VT treatment plan was delivered twice under cone-beam CT guidance and cumulative stationary doses to multi-point PSDs were evaluated. No artifacts were observed on any images acquired during phantom operation. Phantom excursions measured 49.3±25.8%/66.9±14.0%, 97.0±2.2%/96.4±1.7%, and 90.4±4.8%/89.3±3.5% of prescription for cardiac, respiratory, and cardio-respiratory motion profiles for the 2-chamber (PSD) and 12-substructure (IC) phantom modules respectively. In the gated experiments, the cumulative dose was<2% from expected using the IC module. Real-time dose measured for the PSDs at 10Hz acquisition rate demonstrated the ability to detect the dosimetric consequences of cardiac, respiratory, and cardio-respiratory motion when sampling of different locations during a single delivery, and the stability of our phantom dosimetric results over repeated cycles for the high dose and high gradient regions. For the VT delivery, high dose PSD was<1% from expected (5-6 cGy deviation of 5.9Gy/fraction) and high gradient/low dose regions had deviations<3.6% (6.3 cGy less than expected 1.73Gy/fraction). A novel multi-modality modular heart phantom was designed, constructed, and used for gated radiotherapy experiments on a 0.35 T MR-linac. Our phantom was capable of mimicking cardiac, cardio-respiratory, and respiratory motion while performing dosimetric evaluations of gated procedures using IC and PSD configurations. Time-resolved PSDs with small sensitive volumes appear promising for low-amplitude/high-frequency motion and multi-point data acquisition for advanced dosimetric capabilities. Illustrating VT planning and delivery further expands our phantom to address the unmet needs of cardiac applications in radiotherapy.

Design, construction, and dosimetry of 3D printed heterogeneous phantoms for synchrotron brain cancer radiation therapy quality assurance

Objective. This study aims to design, manufacture, and test 3D printed quality assurance (QA) dosimetry phantoms for synchrotron brain cancer radiation therapy at the Australian synchrotron. Approach. Fabricated 3D printed phantoms from simple slab phantoms, a preclinical rat phantom, and an anthropomorphic head phantom were fabricated and characterized. Attenuation measurements of various polymers, ceramics and metals were acquired using synchrotron monochromatic micro-computed tomography (CT) imaging. Polylactic acid plus, VeroClear, Durable resin, and tricalcium phosphate were used in constructing the phantoms. Furthermore, 3D printed bone equivalent materials were compared relative to ICRU bone and hemihydrate plaster. Homogeneous and heterogeneous rat phantoms were designed and fabricated using tissue-equivalent materials. Geometric accuracy, CT imaging, and consistency were considered. Moreover, synchrotron broad-beam x-rays were delivered using a 3 Tesla superconducting multipole wiggler field for four sets of synchrotron radiation beam qualities. Dose measurements were acquired using a PinPoint ionization chamber and compared relative to a water phantom and a RMI457 Solid Water phantom. Experimental depth doses were compared relative to calculated doses using a Geant4 Monte Carlo simulation. Main results. Polylactic acid (PLA+) shows to have a good match with the attenuation coefficient of ICRU water, while both tricalcium phosphate and hydroxyapatite have good attenuation similarity with ICRU bone cortical. PLA+ material can be used as substitute to RMI457 slabs for reference dosimetry with a maximum difference of 1.84%. Percent depth dose measurement also shows that PLA+ has the best match with water and RMI457 within ±2.2% and ±1.6%, respectively. Overall, PLA+ phantoms match with RMI457 phantoms within ±3%. Significance and conclusion. The fabricated phantoms are excellent tissue equivalent equipment for synchrotron radiation dosimetry QA measurement. Both the rat and the anthropomorphic head phantoms are useful in synchrotron brain cancer radiotherapy dosimetry, experiments, and future clinical translation of synchrotron radiotherapy and imaging.

Development and verification of a Geant4 model of the electron beam mode in a clinical linear accelerator

At present, a significant number of studies are focused on the development of novel methodologies for the fabrication of dosimetry phantoms. One of these methods is to produce heterogeneous samples by 3D printing. In order to select the most appropriate parameters for such products, it is necessary to conduct numerical simulations. In this work, we developed the model of a beam-forming system using a medical linear accelerator as a reference. This model was used to determine simulation parameters and corresponding dose distributions of an electron beam with nominal energies of 6, 12, and 15 MeV in a homogeneous water phantom. These parameters were, in fact, adapted to provide maximum agreement between simulated distributions and those experimentally obtained with the clinical linear accelerator. The beam simulation was performed using the Geant4 Monte Carlo toolkit. The simulation geometry of the accelerator treatment head includes scattering foil and a flattening filter, which are designed for electron beam broadening. Additionally, the beam-forming system was incorporated to collimate the beam to the required size. A metal applicator was included to reduce the contribution of electron scattering in air. The main simulation parameters were iteratively tuned by comparing simulation results with experimentally obtained data. It is shown that the simulated percentage depth dose and transverse profiles for electron beams in water phantom are in good agreement with the experimental data obtained with a cylindrical ionization chamber. This demonstrates that the methodology employed in the development of the numerical model of the medical linear accelerator is vendor-independent, readily implementable, and allows for rapid calculations. Furthermore, the model can be applied for a variety of purposes, including the selection of parameters for the fabrication of heterogeneous dosimetry phantoms.

RFPID: development and 3D-printing of a female physical phantom for whole-body counter

Whole-body counters (WBC) are used in internal dosimetry for in vivo monitoring in radiation protection. The calibration processes of a WBC set-up include the measurement of a physical phantom filled with a certificate radioactive source that usually is referred to a standard set of individuals determined by the International Commission on Radiological Protection (ICRP). The aim of this study was to develop an anthropomorphic and anthropometric female physical phantom for the calibration of the WBC systems. The reference female computational phantom of the ICRP, now called RFPID (Reference Female Phantom for Internal Dosimetry) was printed using PLA filament and with an empty interior. The goal is to use the RFPID to reduce the uncertainties associated with in vivo monitoring system. The images which generated the phantom were manipulated using ImageJ®, Amide®, GIMP® and the 3D Slicer® software. RFPID was split into several parts and printed using a 3D printer in order to print the whole-body phantom. The newly printed physical phantom RFPID was successfully fabricated, and it is suitable to mimic human tissue, anatomically similar to a human body i.e., size, shape, material composition, and density.

Evaluating polyester resin as a viable substitute for PMMA in computed tomography dosimetry phantoms

The current study aimed to evaluate the suitability of polyester resin as an alternative material to polymethyl methacrylate (PMMA) for computed tomography (CT) dosimetry phantoms using the GEANT4/GATE Monte Carlo simulation platform. Cylindrical phantoms (32 cm diameter) constructed of polyester resin and PMMA were simulated and compared in terms of atomic composition, effective atomic number, electron density, mass density, and photon interaction mechanisms. Weighted CT dose index (CTDIw) values were calculated for each phantom at 80, 110, and 130 kVp tube voltages based on measurements of CTDI100,c and CTDI100,p. Results demonstrated that the physical properties of polyester closely matched those of PMMA, and the polyester phantom displayed equivalent dosimetric behavior to the PMMA phantom at all tube voltages tested. CTDIw values from the polyester phantom were within 1.4 % of the PMMA phantom across all tube voltages. Conversion coefficients were derived to equate polyester CTDIw values to PMMA dose equivalents. This study found that a polyester resin phantom exhibited radiation dosimetry commensurate with the standard PMMA phantom for CT dose assessment. Consequently, polyester resin represents a viable substitute material when PMMA is unavailable for construction of CT dosimetry phantoms.

Comparing tissue-equivalent properties of polyester and epoxy resins with PMMA material using Gate/Geant4 simulation toolkit

This study investigates the applicability of cost-effective and commercially available polyester and epoxy resins as alternative materials for polymethyl methacrylate (PMMA) in computed tomography (CT) dosimetry phantoms. The mass attenuation coefficients (μ/ρ) of the resin samples were determined using the GEANT4/GATE simulation framework and compared with those of PMMA material over a spectrum of diagnostic photon energies from 10 to 150 keV. A CT scanner was used to acquire the mean attenuation values (CT number) of the fabricated samples at 80,100,120 and 140 kVp CT tube energy. The study found that the resins have similar physical properties and dosimetry behavior to PMMA at all energies. Polyester has a negligible 1% deviational variance in mass attenuation from PMMA. Epoxy demonstrates substantially elevated mass attenuation coefficients compared to PMMA at inferior photon energies between 10 and 40 Kvp. However, with ascending photon energy, the mass attenuation coefficients of epoxy resin and PMMA become more homologous, ultimately converging indistinguishably at 100 Kvp. The CT number results showed that polyester has a 3% difference from PMMA. Moreover, the epoxy resin's CT numbers were within 18HU of PMMA material. These findings demonstrate the feasibility of using low-cost, readily available resin composites such as polyester and epoxy resins as a substitute material for CT dosimetry phantom in computed tomography.

Development and validation of the low-cost pregnant female physical phantom for fetal dosimetry in MV photon radiotherapy.

Monte Carlo (MC) simulations or measurements in anthropomorphic phantoms are recommended for estimating fetal dose in pregnant patients in radiotherapy. Among the many existing phantoms, there is no commercially available physical phantom representing the entire pregnant woman. In this study, the development of a low-cost, physical pregnant female phantom was demonstrated using commercially available materials. This phantom is based on the previously published computational phantom. Three tissue substitution materials (soft tissue, lung and bone tissue substitution) were developed. To verify Tena's substitution tissue materials, their radiation properties were assessed and compared to ICRP and ICRU materials using MC simulations in MV radiotherapy beams. Validation of the physical phantom was performed by comparing fetal doses obtained by measurements in the phantom with fetal doses obtained by MC simulations in computational phantom, during an MV photon breast radiotherapy treatment. Materials used for building Tena phantom are matched to ICRU materials using physical density, radiation absorption properties and effective atomic number. MC simulations showed that percentage depth doses of Tena and ICRU material comply within 5% for soft and lung tissue, up to 25cm depth. In the bone tissue, the discrepancy is higher, but again within 5% up to the depth of 5cm. When the phantom was used for fetal dose measurements in MV photon breast radiotherapy, measured fetal doses complied with fetal doses calculated using MC simulation within 15%. Physical anthropomorphic phantom of pregnant patient can be manufactured using commercial materials and with low expenses. The files needed for 3D printing are now freely available. This enables further studies and comparison of numerical and physical experiments in diagnostic radiology or radiotherapy.

Deterioration of 3D printed multicomponent radiotherapy dosimetry phantom’s properties upon high energy irradiation

Accuracy and realization of the prescribed dose in radiotherapy is one of the crucial ways to ensure the quality of the treatment, which usually is closely related to the use of different types of phantoms. Nowadays 3D printing technology is a promising methodology for the fabrication of phantoms, mimicking different biological tissues. Therefore, analysis of the structural properties of materials and their deterioration due to the irradiation is an important issue. This study is aimed to assess radiation-induced changes of the physical and mechanical properties of 3D printed materials used in the construction of the advanced multicomponent dosimetry phantom for radiotherapy when high energy (6 MeV) X-ray photons were applied for irradiation. Irradiation dose of 70 Gy, representing total dose delivered to the target during the whole treatment procedure prescribed for a patient was applied. Composites filaments with TiO2 additive were extruded using a 3D Devo filament extruder and experimental samples were printed using 3D printer Zortrax M300. Attenuation properties of the samples were simulated using the XCOM database, while mechanical tests were performed using the ElectroPuls® E10000 Linear-Torsion machine. It was observed that 6 MeV photons irradiation of the investigated composites (polyethylene terephthalate glycol (PETG), Polylactic acid (PLA), High Impact Polystyrene (HIPS), ULTRAT ABS and GLASS) and PLA containing various concentrations of TiO2 additives (0 %, 0.5 %, 1.0 % and 2.0 %)) has not induce d significant deterioration of samples’ attenuation and mechanical properties, indicating variations within interval of 5 % − 10 %. However, performed investigation also revealed some improvement of structural and mechanical properties of 3D printed PLA composites with incorporated TiO2.

Pembuatan In-House Phantom untuk Pengukuran Image Quality dan Dosimetri Sebagai Tool Optimasi Protokol Pemeriksaan CT Scan Thorak

The computed tomography scanner (CT scan) protocol used in patient examinations must be continuously reviewed and optimized. Medical physicists evaluate the quality of the resulting image using an image quality phantom and evaluate radiation dose using a dosimetry phantom separately. Procuring a dosimetry phantom and image quality phantom for CT scans separately also requires a lot of money. Therefore, developing a dosimetry phantom and image quality phantom combined in one phantom is expected to be a solution to overcome the mentioned problem. This research aims to create a phantom as a combination of a dosimetry phantom and an image quality phantom and to obtain an optimal CT scan protocol so that informative images can be obtained with minimal doses. The phantom that is made resembles the thoracic organs. The dose length product (DLP) and size-specific dose estimates (SSDE) measured from the phantom were compared with those from 100 patient images for chest CT scan examinations from January to December 2022 and measured using IndoseCT.The image quality of the phantom was measured using IndoQCT software. The estimated dosimetry data from the phantom are 122,5 mGy.cm and 10,94 mGy for DLP and SSDE, respectively, while the DLP and SSDE from patients are 143,5 mGy.cm and 9 mGy. Image quality test results for uniformity with a maximum difference in CT number of 4 HU. Maximum noise is 38,1 HU, and the minimum is 30 HU. The geometric accuracy measurement results are 0,4 mm from the actual size. Spatial Resolution of 0,8 lp/mm. The R2 value of contrast linearity is 0,9972. The Modulation Transfer Function (MTF10) measurement results are 0,63 mm--1. The results of the slice thickness test show the suitability between the measured results and the slice thickness setting on the CT Scan. An in-house phantom can be used in dosimetry and image quality measurements to optimize the thoracic CT scan protocol. Keywords: In-house phantom, Image quality, Dosimetry, Optimization

Eye radiation dose from breast cancer screening using full field digital mammography and digital breast tomosynthesis: A phantom study

IntroductionThe eye lens is recently classified as one of the most radiosensitive tissues by the International Commission on Radiological Protection (ICRP), and it has been suggested that the eye lens receives radiation dose during mammography due to scatter radiation. The aim of this study was to investigate the radiation dose received by the lens of the clients’ eye from Full Field Digital Mammography (FFDM) and Digital Breast Tomosynthesis (DBT) screening. MethodsThe eye radiation dose received by ATOM dosimetry phantom was estimated with thermo-luminescent dosemeters (TLDs). One TLD was utilised for each eye. A breast phantom was exposed for four-view screening mammography using 16 FFDM machines and one DBT machine. The breast phantom was exposed three times for each mammographic position and an average TLD dose reading was considered to minimise random error. ResultsFor four-view FFDM screening, the phantom eye radiation dose ranges from 0.013 mGy to 0.029 mGy with a mean±sd of 0.019 ± 0.005 mGy. A higher eye radiation dose of 0.041 mGy was recorded from four-view DBT screening. The statistical analysis demonstrated that the eye lens radiation dose is strongly and significantly correlated to breast organ dose and X-ray tube voltage. ConclusionThe phantom eye lens was exposed to scatter radiation from FFDM and DBT screening. The measured dose via the four-view DBT screening was higher than the four-view FFDM screening, but sits below the internationally acceptable ranges. If the findings of our paper hold true in practice, then the risk to the lens of the eyes for women attending breast screening is acceptable. Implications for practiceThe new lens radiation dose levels recommended by the ICRP necessitate the reevaluation of eye radiation dose from different radiographic examinations, especially those used for screening purpose where healthy individuals involved.

One approach for selection of materials available for 3D printing of a dosimetry pelvic phantom: numerical simulation

Pelvic organ tumors are a serious problem in the field of oncology and account for one-third of the total number of the most common locations of neoplasms. Radiation therapy is often used to treat these types of cancer. A necessary procedure in the application of radiation therapy is the verification of the dosimetric plan to ensure maximum accuracy of radiation and minimize the negative effects of overexposure. To achieve these goals, dosimetry phantoms are used to mimic the structure and properties of biological tissues. Additive technologies can be an effective method for manufacturing such phantoms due to their high-precision ability to replicate both body geometry and anatomical structures. Today, the search and development of materials suitable for both additive technologies and assessing the interaction of ionizing radiation with matter is a relevant task. In this study, models of biological tissues and organs, as well as materials for 3D printing, were created. The features of Co-60 photon beam interaction with these materials were analyzed by numerical simulation. The calculated results demonstrated the suitability of plastic materials based on polylactide for simulating individual biological tissues and human organs from the point of view of interaction with ionizing radiation.

Evaluation of the water-equivalent characteristics of the SP34 plastic phantom for film dosimetry in a clinical linear accelerator.

In this study, some confusing points about electron film dosimetry using white polystyrene suggested by international protocols were verified using a clinical linear accelerator (LINAC). According to international protocol recommendations, ionometric measurements and film dosimetry were performed on an SP34 slab phantom at various electron energies. Scaling factor analysis using ionometric measurements yielded a depth scaling factor of 0.923 and a fluence scaling factor of 1.019 at an electron beam energy of <10 MeV (i.e., R50 < 4.0 g/cm2). It was confirmed that the water-equivalent characteristics were similar because they have values similar to white polystyrene (i.e., depth scaling factor of 0.922 and fluence scaling factor of 1.019) presented in international protocols. Furthermore, percentage depth dose (PDD) curve analysis using film dosimetry showed that when the density thickness of the SP34 slab phantom was assumed to be water-equivalent, it was found to be most similar to the PDD curve measured using an ionization chamber in water as a reference medium. Therefore, we proved that the international protocol recommendation that no correction for measured depth dose is required means that no scaling factor correction for the plastic phantom is necessary. This study confirmed two confusing points that could occur while determining beam characteristics using electron film dosimetry, and it is expected to be used as basic data for future research on clinical LINACs.

Experimental Investigation of X-Ray Radiation Shielding and Radiological Properties for Various Natural Composites.

Shielding from radiation and plan dose verification is vital during the potential applications in industrial and medical applications. A number of natural composites have been investigated for protecting against high-energy X-ray shielding. The aim is to learn about how natural composites behave under various X-ray energies at STP. The radiological parameters of wood samples were determined using computed tomography imaging, specifically relative electron density (RED), Hounsfield units (HUs), and mass density (MD). Percentage attenuation was measured using a semiflux ionization chamber incorporated with a brass build-up cap and an ionization chamber placed at the beam Isocenter for a different type of natural composite. Measurements are being carried out on a Linear accelerator at an SSD of 110 cm with different collimator sizes. Measured values of HUs, RED, and MD were -232 ± 40, 0.738 ± 0.039, 0.768 ± 0.024 g/cc,-368 ± 41, 0.662 ± 0.047, 0.632 ± 0.024 g/cc, -334 ± 44, 0.639 ± 0.042, 0.666 ± 0.026 g/cc, -370±61, 0.604±0.059, 0.63± 0.036 g/cc, -433±39, 0.543±0.038, 0.608 ± 0.035 g/cc, -382±54, 0.5±0.052, 0.618 ± 0.0316 g/cc, -292±68, 0.680±0.066, 0.708 ± 0.039 g/cc, -298±27, 0.680±0.0229, 0.702± 0.131 g/cc, for Acacia Nilotica, Mangifera Indica, Azadirachta Indica, Tectona Grandis L, Ficus Religiosa, Tecomella Undulata, Sesamum Indicum, Pinus respectively. Measurements show that attenuation is affected by the energy of incident photons, collimator opening, and the type of density of the wood. Various radiological parameters were determined for wood samples that can be utilized to create inhomogeneous phantoms in dosimetry. The largest attenuation is found in Acacia Nilotica and Sesamum Indicum, while the lowest attenuation is found in Ficus religiosa.

Development of a quasi-3D dosimeter using radiochromic plastic for patient-specific quality assurance.

Patient-specific QA verification ensures patient safety and treatment by verifying radiation delivery and dose calculations in treatment plans for errors. However, a two-dimensional (2D) dose distribution is insufficient for detecting information on the three-dimensional (3D) dose delivered to the patient. In addition, 3D radiochromic plastic dosimeters (RPDs) such as PRESAGE® represent the volume effect in which the dosimeters have different sensitivities according to the size of the dosimeters. Therefore, to solve the volume effect, a Quasi-3D dosimetry system was proposed to perform patient-specific QA using predetermined-sized and multiple RPDs. For patient-specific quality assurance (QA) in radiation treatment, this study aims to assess a quasi-3D dosimetry system using an RPD. Gamma analysis was performed to verify the agreement between the measured and estimated dose distributions of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). We fabricated cylindrical RPDs and a quasi-3D dosimetry phantom. A practicability test for a pancreatic patient utilized a quasi-3D dosimetry device, an in-house RPD, and a quasi-3D phantom. The dose distribution of the VMAT design dictated the placement of nine RPDs. Moreover, a 2D diode array detector was used for 2D gamma analysis (MapCHECK2). The patient-specific QA was performed for IMRT, VMAT, and stereotactic ablative radiotherapy (SABR) in 20 prostate and head-and-neck patients. For each patient, six RPDs were positioned according to the dose distribution. VMAT SABR and IMRT/VMAT plans employed a 2%/2mm gamma criterion, whereas IMRT/VMAT plans used a 3%/2mm gamma criterion, a 10% threshold value, and a 90% passing rate tolerance. 3D gamma analysis was conducted using the 3D Slicer software. The average gamma passing rates with 2%/2mm and 3%/3 mm criteria for relative dose distribution were 91.6%±1.4% and 99.4%±0.7% for the 3D gamma analysis using the quasi-3D dosimetry system, respectively, and 97.5% and 99.3% for 2D gamma analysis using MapCHECK2, respectively. The 3D gamma analysis for patient-specific QA of 20 patients showed passing rates of over 90% with 2%/2mm, 3%/2mm, and 3%/3mm criteria. The quasi-3D dosimetry system was evaluated by performing patient-specific QAs with RPDs and quasi-3D phantom. The gamma indices for all RPDs showed more than 90% for 2%/2mm, 3%/2mm, and 3%/3mm criteria. We verified the feasibility of a quasi-3D dosimetry system by performing the conventional patient-specific QA with the quasi-3D dosimeters.

X-ray spectrometry applied for determination of linear attenuation coefficient of polymer-based samples as radiologically tissue-equivalent materials

In this work we obtained experimental linear attenuation coefficients of polymer-based samples at diagnostic imaging energy range (15-150 keV) for eleven formulations candidates for tissue-equivalent materials (TEMs). TEMs is any material that simulates a human body part or human tissue in its interaction with radiation. In diagnostic radiology, the maximum difference between the linear attenuation coefficient of the TEMs and the target material should be no more than 5% in the energy range of interest. A polienergetic narrow beam was obtained using a tungsten target x-ray tube and CdTe detector. The densities of the samples were determined and compared with reference materials obtaining a maximum difference of 17%. The comparisons between the linear attenuation coefficient of the formulations and the respective reference materials for which they were initially designed, has demonstrated good correspondence over a wide energy range. Energy ranges in which the developed samples simulate other human tissues in addition to those initially considered were found, taken into account the criterion that the maximum difference between the linear attenuation coefficients does not exceed 5% is met. The results emphasize the possibility of production and characterization of TEMs to be used in the construction of imaging and dosimetry phantoms.

Development of optimised tissue-equivalent materials for proton therapy

Objective. In proton therapy there is a need for proton optimised tissue-equivalent materials as existing phantom materials can produce large uncertainties in the determination of absorbed dose and range measurements. The aim of this work is to develop and characterise optimised tissue-equivalent materials for proton therapy. Approach. A mathematical model was developed to enable the formulation of epoxy-resin based tissue-equivalent materials that are optimised for all relevant interactions of protons with matter, as well as photon interactions, which play a role in the acquisition of CT numbers. This model developed formulations for vertebra bone- and skeletal muscle-equivalent plastic materials. The tissue equivalence of these new materials and commercial bone- and muscle-equivalent plastic materials were theoretical compared against biological tissue compositions. The new materials were manufactured and characterised by their mass density, relative stopping power (RSP) measurements, and CT scans to evaluate their tissue-equivalence. Main results. Results showed that existing tissue-equivalent materials can produce large uncertainties in proton therapy dosimetry. In particular commercial bone materials showed to have a relative difference up to 8% for range. On the contrary, the best optimised formulations were shown to mimic their target human tissues within 1%–2% for the mass density and RSP. Furthermore, their CT-predicted RSP agreed within 1%–2% of the experimental RSP, confirming their suitability as clinical phantom materials. Significance. We have developed a tool for the formulation of tissue-equivalent materials optimised for proton dosimetry. Our model has enabled the development of proton optimised tissue-equivalent materials which perform better than existing tissue-equivalent materials. These new materials will enable the advancement of clinical proton phantoms for accurate proton dosimetry.

Development of anthropomorphic computational phantoms at the UFPE

To evaluate the amount of energy deposited in radiosensitive organs and tissues of the human body, when an anthropomorphic phantom is irradiated, researchers in numerical dosimetry use the so-called exposure computational models (ECMs). One can imagine an ECM as a virtual scene composed of a phantom in a mathematically defined position in relation to a radioactive source. The source in these ECMs produces the initial state of the simulation: the position, direction, and energy with which each particle enters the phantom are essential variables. For subsequent states of a particle history, robust Monte Carlo (MC) codes are used. For the subsequent states of a particle's history, robust Monte Carlo (MC) codes are used, which simulate the average free path that the particle performs without interacting, its interaction with the atoms in the medium and the amount of energy deposited per interaction. MC codes also evaluate normalization quantities, so the results are printed in text files in the form of conversion coefficients between the absorbed dose and the selected normalization quantity. From the 2000s, the authors have published ECMs where a voxel phantom is irradiated by photons in the environment of the MC code EGSnrc (EGS = Electron Gamma Shower; nrc = National Research Council Canada). The production of articles, dissertations and theses required the use of specific computational tools, such as the FANTOMAS, DIP (Digital Image Processing) and Monte Carlo applications, for the various steps of numerical dosimetry, which ranges from the preparation of input files to the execution from the ECM to the organization and graphical and numerical analysis of the results. This article reviews computational phantoms for dosimetry mainly those produced in DEN-UFPE dissertations and thesis.